A butt jointing method is one of methods of integrating a plurality of waveguide-type optoelectronic elements, such as semiconductor lasers and optical modulators, with a single InP substrate. The butt jointing method joints a plurality of optical waveguides arranged on a single substrate with their axes aligned in an end-to-end joining fashion. The butt jointing method repeats a processing cycle including the steps of forming a first optical waveguide on a semiconductor substrate by crystal growth, partly coating the first optical waveguide with a mask pattern, removing an uncoated part of the first optical waveguide by an etching process, and connects a second optical waveguide to the first optical waveguide by growing the second optical waveguide by metal organic vapor-phase epitaxy (MOVPE) in a space from which the uncoated part of the first optical waveguide has been removed by necessary times. Using this butt jointing method makes it possible to optimize the material, composition, the number of layers and film thickness of each multilayer optical waveguide structure. Therefore, as compared with a selective growth method that builds a plurality of waveguide-type optoelectronic elements simultaneously by a single cycle of a selective growth process, the butt jointing method is a suitable method of fabricating a high-performance integrated optoelectronic device. The optoelectronic waveguide is a multilayer optoelectronic waveguide structure built by sandwiching a core layer between cladding layers having a refractive index smaller than that of the core layer. In a waveguide-type optoelectronic device having a core layer made of an InGaAlAs material or an InGaAsP material, an InP substrate can serve as the cladding layer contiguous with the substrate.
The characteristic of a known multiple butt-joint type laser built by combining a plurality of InGaAlAs multiple quantum well type laser waveguide layers and a plurality of InGaAsP bulk waveguide layers and the results of examination of the optical coupling efficiency of the butt-jointed joints of the multiple butt-joint type laser are mentioned in IEEE Photonics Technology letters, Vol. 17, p. 1148 (Non-patent document 1). A known integrated optoelectronic device having a third optical waveguide formed in a space formed by removing a defective layer having many crystalline defects and formed between the first waveguide-type optoelectronic element and the second waveguide-type optoelectronic element is disclosed in JP-A No. 324936/2002 (Patent document 1).